1, X-ray X-ray is a very penetrating ray, a high-energy light particles, so the general object can not be blocked, the ray to be blocked, the key by the ray intensity, frequency, blocking material and the degree of the role of the ray, the thickness of the blocking material, blocking the size of the material to decide together. In general, the common X-ray (for hospitals) about 3~5cm of lead can be blocked. However, it will also show the shadow shape of the blocking material on the background screen, just like a solar eclipse, although it blocks the sunlight, but leaves a shadow. Now the current big hospital CR and DR is the use of X-ray absorption, two-dimensional imaging. 2, CT CT is a full-featured condition detection instruments, it is the electronic computerized X-ray tomography technology referred to. CT’s working procedure is this: it is based on the different tissues of the human body on the X-ray absorption and transmission rate of different, the application of highly sensitive instruments on the human body for measurement, and then the measurement of the data obtained into the electronic computer, the electronic computer to process the data, can be ingested by the human body to be examined part of the cross-section or three-dimensional image, to find any part of the body of the small lesions. 3, magnetic resonance MRI is also known as magnetic resonance imaging, the reason why later not known as nuclear magnetic resonance and renamed magnetic resonance, because the Japanese scientists put forward its country is highly harmed by nuclear weapons, in order to show respect for the nuclear word removed. Nuclear magnetic resonance is a physical phenomenon, as a means of analysis is widely used in the fields of physics, chemistry biology, etc., until 1973 it was used for medical clinical testing. To avoid confusion with radiologic imaging in nuclear medicine, it is referred to as magnetic resonance imaging (MR). MR is a biomagnetic spin imaging technology, it is the use of atomic nuclei spin movement characteristics, in the applied magnetic field, the radio frequency pulse excitation after the generation of signals, detector detection and input into the computer, after processing and conversion in the screen to display images. Advantages: (1) MRI has no damage to the human body; (2) MRI can obtain a three-dimensional image of the brain and spinal cord, unlike CT, layer by layer scanning and may miss the lesions; (3) can diagnose cardiac lesions, CT due to the slow speed of scanning and is difficult to perform; (4) on the bladder, rectum, uterus, vagina, bones, joints, muscles, and other parts of the examination is better than the CT. Disadvantages: (1) and the same as the CT Disadvantages: (1) Like CT, MRI is also diagnostic imaging, and many lesions are still difficult to be diagnosed by MRI alone, unlike endoscopy, which can obtain both imaging and pathological diagnosis; (2) the examination of the lungs is not superior to X-ray or CT, and the examination of the liver, pancreas, adrenal glands, and prostate is not superior to CT, but the cost is much higher; (3) lesions in the gastrointestinal tract are not as good as endoscopy; (4) those who keep metal objects in the body should not undergo MRI. (4) the body retains metal objects should not receive MRI. (5) Critically ill patients can not be done (6) pregnancy within three months (7) with a pacemaker 4, PET PET full name: positron emission computed tomography (Positron Emission Computed Tomography), is the field of nuclear medicine is more advanced clinical examination of imaging technology. It is the only new imaging technology that can show the metabolism of biomolecules, receptors and neuromediators activities in living body, and is now widely used in the diagnosis and differential diagnosis of a variety of diseases, judgment of the condition, evaluation of the efficacy of the treatment, organ function research and development of new drugs and other aspects. The imaging principles of the first three are fundamentally different. (1) High sensitivity: PET is a kind of imaging reflecting molecular metabolism, when the disease is in the early stage of molecular level changes, the morphology and structure of the lesion area has not yet presented abnormalities, MRI, CT examination can not be a clear diagnosis, PET examination can be found where the lesion is, and can obtain three-dimensional image, but also can be quantitatively analyzed, to achieve an early diagnosis, which is currently incomparable to other imaging examinations. (2) High specificity: It is difficult to judge whether a tumor is benign or malignant when it is found in organs by MRI and CT examination, but PET examination can make a diagnosis according to the characteristics of high metabolism of malignant tumors. (3) Whole-body imaging: PET can obtain images of all areas of the body in one-time whole-body imaging. (4) Good safety: The nuclide needed for PET examination has a certain degree of radioactivity, but the amount of nuclide used is very small, and the half-life is very short (the short one is about 12 minutes, and the long one is about 120 minutes), and after physical attenuation and biological metabolism, it will remain in the body of the examined person for a short period of time. The radiation exposure dose of a PET whole-body examination is much smaller than that of a conventional CT examination of a part of the body, which is safe and reliable. 5, PET / CT and we are currently using PET / CT is the perfect combination of PET and CT technology, complement each other. PET / CT this combination of technologies can greatly improve the accuracy of clinical diagnosis (such as the need for a single isolated small foci in the body of benign and malignant differential diagnosis and pre-surgical localization, etc.), including the precise location and characterization, etc., other tests can not be compared to From the beginning of 2000, the industry has solved the problem of PET / CT, the body of the patient’s radiation exposure is much smaller than a part of the conventional CT examination, and therefore safe. Since 2000, the industry has solved the problem of integrating PET and CT equipment for synchronized scanning. PET/CT can not only solve the problem of synchronized scanning, but at the same time, the density map obtained from CT scanning can be used for scattering correction, which can greatly improve the precision and diagnostic accuracy. Currently, the most advanced equipment can achieve 52-ring PET with 64-slice CT integration (e.g., Siemens Biograph 64), which can be used for precise localization of cardiac function and malignant lesions through synchronization with ECG (termed gating) and manual ECG editing and reconstruction to take into account cardiac arrhythmia.